1. Field of the Invention
This invention relates generally to detecting a lash crossing in a motor vehicle driveline particularly with the use of a device that produces signals indicating the magnitude of torque being transmitted and the directional sense of the transmitted torque.
2. Description of the Prior Art
Automotive drivetrains include meshed gear teeth that exhibit deadband when the direction of torque applied to them changes, as shown in the diagram of FIG. 1 and in FIG. 2.
Such deadband causes discontinuity of the transmitted torque and excitation of the driveline, as the shafts feature certain compliance. Due to that, the deadband is typically called “backlash” or being in the deadband zone during the change of direction of torque: “lash crossing.” If there were no backlash associated with the meshed gears, the shaft twist to torque relationship could have been expressed using the torsional spring equation (Hooke's law): t=Ks q, where Ks is the shaft stiffness.
Lash crossing has been one of the key factors contributing to drivability issues. There has been a continuing effort in the automotive control engineering community to address the problem of backlash via predicting, detecting, avoiding, and mitigating the effects of lash crossing.
Using the measurements available on production vehicles today, reliable detection of the crossing the deadband zone is a formidable challenge. Various publications explore the Hooke's law to derive the driveline torque based on shaft position sensors, which are typically used for angular speed and known as “speed sensors.” Others use the speed difference across the unlocked torque converter as an indication of torque direction at the input of the gearbox.
The numerical and resolution problems associated with estimation methods solely based on speed sensors position (tooth count) readings, remain limited to higher speed operation and are sensitive to various noise factors: synchronization, resolution at low speeds, engine and road disturbances, measurement and numerical errors, to name a few.